1. Field of the Invention
The present invention relates to a microscope and a microscope observing method.
2. Related Background Art
In the physiological field, living cells and living tissues are often studied by use of a microscope. If an observation object is thick, there is a problem in that a deep part of a sample is hard to observe in term of light transmissibility, whereas an area from an objective-lens-side surface of the sample down to a slightly internal part is readily observable.
According to another technique practiced in the physiological field, an electrode image is observed through operation such as bringing a micro-electrode into contact with a local part of the sample or pricking the local part with the micro-electrode by use of a micro-manipulator. When observed in such a way, the electrode is manipulated with respect to the sample above a container containing the sample. In this case, a good sample image of even a thick sample and an electrode image are to be simultaneously observed, and hence an erecting type of microscope is often used. Further, a sample of a living body maybe immersed into an artificial body fluid contained in a chamber, and is observed through this body fluid.
As the study becomes more complicated, a plurality of micro-manipulators fitted with the micro-electrodes are disposed along the periphery of the objective lens. When setting the micro-electrode, to begin with, rough setting is performed by using a low-magnification dry objective lens (with a magnification on the order of, e.g., 4.times., 10.times.) having a wide field, a long working distance and a large depth of focus. Next, final setting or a local observation are carried out by using a high-magnification immersion objective lens (with a magnification on the order of, e.g., 40.times., 60.times.).
The low-magnification dry objective lens has a long working distance, and therefore a front edge of the objective lens exists upwardly of an edge of the chamber containing the sample. A front edge of the high-magnification immersion objective lens exists, however, in the liquid or in the vicinity of a liquid surface and downwardly of the edge of the chamber.
Accordingly, a problem is that the immersion objective lens impinges upon the edge of the chamber when changing over the magnification. Japanese Utility Model Laid-Open Publication No. 6-4720 discloses a microscope capable of obviating the problem without vertically moving the focusing mechanism. This microscope includes vertical moving mechanisms for making the respective objective lenses movable in the optical axis direction, which are provided between an objective lens exchanging unit and the plurality of objective lenses.
According to the prior art described above, the vertical moving mechanism is provided for each objective lens, and hence the construction is complicated, and can make the changeover operation laborious. Further, when trying to ensure a parfocal state with respect to each objective lens, a working precision of the vertical moving mechanism is highly strict, and a price of the product becomes too high to be realistic.
Moreover, in the case of simultaneously observing both of the sample set on the bottom of the chamber containing liquid (e.g., water) and the micro-electrode fitted to the micro-manipulator, there are used the low-magnification dry objective lens for rough setting and the high-magnification immersion objective lens for a minute observation. The sample and the manipulator are observed by the low-magnification dry objective lens throughout a whole depth of the liquid, and the sample is also observed by the high-magnification immersion objective lens through a fixed level of water (liquid) depth based on a design value.
A problem is presented in a case where the sample (chamber) is replaced and a quantity of the water (liquid) in the chamber changes. For the immersion objective lens, a distance from the lens front edge to the sample is in a focusing state at the fixed water (liquid) depth based on the design value. Accordingly, even when the water (liquid) quantity changes, the quantity of the water into which the objective lens front edge is immersed merely changes, and a distance from the sample position to the objective lens fitting position is fixed.
For the observation through the dry objective lens, on the other hand, the distance from the position of the sample in the focusing state to the objective lens fitting position might change due to a difference in refractive index between the water (liquid) and the air.
Consequently, there arises such a problem that both of the dry objective lens and the immersion objective lens are capable of obtaining the parfocal state only when at a given water (liquid) depth based on the design value.
If the water depth changes by 1 mm, it follows that the focusing position changes by approximately 0.25 mm in the dry objective lens. Accordingly, it is required that a focusing handle be largely rotated as a control quantity of the focusing quantity of the microscope, corresponding to a slight change in the water depth, resulting in being forced to suffer inconvenience. Further, the focusing handle is hard to operate in the state where the plurality of micro-manipulators are disposed along the periphery of the microscope, and it is desired that the, operation of the focusing handle be as small as possible.